Process for the removal of carbonyl sulfide from liquid petroleum gas

ABSTRACT

A method for the removal of carbonyl sulfide from liquefied petroleum is disclosed. Removal of carbonyl sulfide is accomplished by contacting a liquid petroleum gas stream containing a carbonyl sulfide as an impurity with a calixarene complexing agent as the principal agent for the removal of the carbonyl sulfide.

This application claims the benefit of U.S. Provisional Application No.60/095,237, filed Aug. 4, 1998.

FIELD OF THE INVENTION

This invention relates to a method for purifying liquefied petroleumgas. More particularly, this invention relates to a process for theremoval of carbonyl sulfide from a liquefied petroleum gas streamutilizing a calixarene as a complexing agent.

BACKGROUND OF THE INVENTION

Liquefied petroleum gas is an important, versatile hydrocarbon fuel andchemical feedstock. It is commercially available as propane orpropane-butane mixtures. It also contains ethane, propylene, isobutane,1-butene, cis- and trans-2-butene, and n-pentane, in minorconcentrations.

Liquefied petroleum gas is generally derived from the refining of crudeoil, and as a by-product of the production of natural gas. Productsderived from these sources, however, are usually contaminated withimpurities such as water, carbon dioxide, and organic sulfur compounds.Such undesirable organic sulfur compounds include, for example, hydrogensulfide, mercaptans, sulfides and carbonyl sulfides.

Carbonyl sulfide was once considered to be a relatively innocuouscontaminant, but is now recognized as being problematic for a variety ofreasons. In particular, carbonyl sulfide can hydrolyze in the presenceof water to form hydrogen sulfide and carbon dioxide. While carbonylsulfide is not itself corrosive, the hydrolysis product, hydrogensulfide, is very corrosive, especially in the presence of water.Consequently, the removal of carbonyl sulfide from liquid petroleumproducts has become increasingly more important to the petroleum fuelprocessing industry.

Prior processes commonly used in the refinery industry for removal ofcarbonyl sulfide from hydrocarbons include (1) treating carbonyl sulfidecontaminants with gas plant solutions of an amine, e.g. mono ethananolamine (MEA), diethanol amine (DEA) and other similar amines; (2)hydrolysis of carbonyl sulfide to CO₂ and H₂S over a catalyst such asactivated alumina, platinum sulfide, Co/Mo and other metals; (3)reaction of carbonyl sulfide with a metal oxides such as, for example.ZnO, CuO/ZnO and PbO; (4) adsorption of carbonyl sulfide on a promotedactivated alumina or molecular sieves such as 4A, 5A and 13X; and (5)reaction of carbonyl sulfide with potassium hydroxide, sodium hydroxideand/or methanol.

Such processes are, however, disadvantageous for various reasons. Forexample, carbonyl sulfide reacts rapidly with primary amines such as MEAand DEA to produce salts that can cause equipment fouling. Processesinvolving hydrolysis of carbonyl sulfide with a catalyst can becomplicated and costly since catalyst selection depends on such factorsas operating temperature, carbonyl conversion, bed size, estimated lifeof catalyst, and the like.

Carbonyl sulfide removal with metal oxides is typically not costeffective for most olefin or refinery applications. Metal oxides aresometimes used in the natural gas industry when the concentration ofsulfur is very low.

Adsorption processes using molecular sieve products are best for bulkcarbonyl sulfide removal at levels of less than 100 ppm where bed outletlevels of 5 ppm are acceptable. Molecular sieve beds for carbonylsulfide removal must be very large with short cycles and highregeneration rates. For an olefin unit, E/P feed applications, bed-cycletime and regeneration gas flow requirements are common removal systemlimits.

Sufnolime™, a solid sodium hydroxide supported on a non-regenerablecalcium hydroxide catalyst, has been used in a fixed bed for removal ofcarbonyl sulfide. Sufnolime™ is microscopic and difficult to remove fromthe bed. Further, the active catalyst is only 10% to 14% of the catalystweight; thus, requiring a relatively large bed size.

Potassium hydroxide is more reactive than sodium hydroxide and canremove greater amounts of carbonyl sulfide in liquid/liquid contactingapplications. Solid potassium hydroxide beds have also been successful.However, potassium hydroxide can be costly and in some cases, noteconomically feasible.

Consequently, there exists a need in the petroleum refining industry forsimple, economical and efficacious processes for the removal of carbonylsulfide from hydrocarbons, in particularly, from a liquefied petroleumgas.

Accordingly, it is an advantage of the present invention to provide aprocess for the removal of carbonyl sulfide from a liquid petroleum gasusing a solid complexing agent.

It is also an advantage of the present invention to provide a processfor the removal of carbonyl sulfide from a liquid petroleum gasutilizing a calixarene complexing agent.

It is a further advantage of the present invention to provide a processfor the selective removal of carbonyl sulfide from liquid petroleum gasstream utilizing a solid calixarene complexing agent.

Additional advantages and objects of the invention will be set forth inpart in the description, and in part will be obvious from thedescription, or may be learned by practice of the invention. Otheradvantages and objects of this invention may be realized and obtained bymeans of the process particularly pointed out in the appended claims.

SUMMARY OF THE INVENTION

We have now discovered that a calixarene selectively reacts withcarbonyl sulfide contained in a liquid petroleum gas stream to form astable complex which can be isolated and removed from the gas stream.The formation of this complex provides the basis for a simple andeconomical process for the removal of carbonyl sulfide from liquefiedpetroleum gas.

Accordingly, the method of the present invention comprises contacting aliquefied petroleum gas stream containing carbonyl sulfide as animpurity with a calixarene complexing agent. The liquefied petroleumstream is contacted with the desired calixarene in an amount sufficientto remove all or substantially all of the carbonyl sulfide contained inthe petroleum stream.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a solid-liquid contactor system useful to perform theprocess of the present invention.

FIG. 2A illustrates a Fourier transform infrared septrum of carbonylsulfide.

FIG. 2B illustrates a Fourier transform infrared septrum ofp-t-butylcalix[4]arene complexed with carbonyl sulfide.

FIG. 2C illustrates a Fourier transform infrared septrum ofp-t-butylcalix[4]arene.

FIG. 3 illustrates a plot detailing the absorbance of carbonyl sulfideby p-t-butylcalix[4]arene as a function of time.

FIG. 4 illustrates a plot detailing the gravimetric decay of carbonylsulfide by p-t-butylcalix[4]arene.

DETAILED DESCRIPTION OF THE INVENTION

The present invention embodies a process wherein carbonyl sulfide isremoved from a liquefied petroleum gas stream by utilizing a solidcalixarene as a complexing agent. In accordance with the process of theinvention, carbonyl sulfide contaminated liquefied petroleum gas isflowed into intimate contact with the calixarene complexing agent. Thecomplexing agent acts to selectively complex carbonyl sulfide and form astable calixarene/carbonyl sulfide complex.

The treated petroleum gas is thereafter removed from the contactor toisolate the gas from the calixarene/carbonyl complex. Once isolated, thecomplex maybe gently heated to release carbonyl sulfide and regeneratethe calixarene for reuse.

As used herein, the expression “liquefied or liquid petroleum gas”refers to a liquid hydrocarbon composition consisting mainly of propaneand/or propane-butane mixtures. The liquid hydrocarbon may also containethane, propylene, isobutane, 1-butene, cis- and trans-2-butane, andn-pentane in minor concentrations.

Suitable calixarene complexing agents useful for practicing the presentinvention include those of formula I:

wherein

R₁,-R_(3+n) are each independently H, primary C₁₋₂₀ alkyl, secondaryC₃₋₂₀ alkyl, tertiary C₄₋₂₀ alkyl, C₁₋₂₀ alkoxy, C₁₋₂₀ thioalkyl, C₆₋₂₀aryl, C₆₋₂₀ aryloxy, C₆₋₂₀ aryl, nitro, halogen and CH₂NR₂ ¹ where R¹ isa C₁₋₂₀ alkyl;

X₁-X_(3+n) are each independently H, OH, SH, C₁₋₂₀ alkoxy, C₁₋₂₀thioalkyl, C₆₋₂₀ aryloxy, OC(O)C₁₋₂₀ alkyl and C₂₋₂₀ alkenyloxy; and

n is an integer of 1 to 5, preferably n is 4.

Preferably, R₁-R_(3+n) may be hydrogen, methyl, ethyl, propyl,isopropyl, butyl, iso-butyl, sec-butyl, tert-butyl, phenyl, xylyl,phenyoxy, naphthyl, benzyl, fluorine, chlorine, bromine and iodine,methoxy, ethoxy, propoxy butoxy, N,N-dimethyl methyleneamine,N-N-diethyl methyleneamine, N,N-dipropyl methyleneamine, N,N-diphenylmethyleneamine, C₆₋₂₀ aryl, NO₂ or CH₂NR¹ ₂ where R¹ is a C₁₋₂₀ alkyl.

Preferably X₁-X_(3+n) may be H, OH, methoxy, ethoxy and propoxy.

More specifically, suitable calixarenes are calix[4]arene andsubstituted derivatives thereof. In a preferred embodiment of theinvention, the calixarene is a para substituted derivative ofcalix[4]arene. Most preferably, the calixarene is para-t-butylcalix[4]arene.

The synthesis of calixarenes and substituted calixarenes is well knownto those of ordinary skill in the art and can be prepared byconventional methods. For example the synthesis of p-phenylcalix[4]areneis described in Juneja et al (J. Am. Chem. Soc. 1993 115:3813-3819). Thesynthesis of p[4-(2-hydroxyethyl) piperazinomethyl]calix[4]arene isdescribed by Atwood et al (Angew. Chem. Int. Ed. Engl. 1993 32:1093-94).

Contact between the liquefied petroleum gas and the complexing agent maybe accomplished using any conventional contactor system which allows oneto intimately mix solid and liquid components. In one embodiment of theinvention, a stream of liquefied petroleum containing carbonyl sulfideas an impurity is flowed into a solid-liquid contactor containing asolid calixarene complexing agent. Suitable solid-liquid contactorsystems include, but are not limited to, packed columns, coated cakes,structured tubes, supports, saddles and the like. Typically, as shown inFIG. 1, the solid-liquid contactor comprises a column (1) having aninlet end (3) and an outlet end (4) for passage of the liquid gasstream, packed with a solid calixarene complexing agent (2).

The flow rate of the liquefied petroleum stream is such to provideeffective contact between the complexing agent and the liquid petroleumgas to remove all or substantially all of the carbonyl sulfide containedin the petroleum gas stream. The selection of the flow rate can easilybe determined by one skilled in the art based on such factors as thenature of the solid-liquid contactor, the concentration of complexingagent present in the contactor, the amount of carbonyl sulfide impurityin the petroleum stream, and the like.

In another embodiment of the present invention, a carbonyl sulfidecontaminated stream of liquefied petroleum gas is flowed into intimatecontact with a calixarene complexing agent, wherein the complexing agentis immobilized on an inert support.

Immobilization of the complexing agent may be accomplished by any meanswherein immobilization does not prevent the calixarene from forming astable complex with carbonyl sulfide. For example, in the case of thecalix[4]arene and derivatives thereof, immobilization may be by couplingthrough the R group, to the immobilized support. The R group may bebonded directly to the immobilized support. Alternatively, binding ofthe calix[4]arene to the immobilized support may be through one of the—OH groups at the para position to the R group.

Suitable inert supports include for example polystrene, polyester,polyamide, poly(meth) acrylate, polyurethane and polyvinyl chloride. Theinert support must be a material such that when the complexing agent isbound to the support, the material does not interfere the complexationreaction of the complexing agent with carbonyl sulfide.

Purification using the immobilized calixarene may be performed using theimmobilized agent as a chromatographic support. The column of theimmobilized complexing agent is contacted with a crude liquefiedpetroleum gas stream under conditions sufficient to form a complex ofthe carbonyl sulfide with the immobilized calixarene complexing agent.

Throughout the process of the invention, the temperature of thecontactor system must be compatible to maintain the liquid petroleum gasin a liquid state. The temperature will vary depending on thecomposition of the petroleum gas. In general, however, the temperatureis maintained at a range of about 40° C. to about 200° C., preferablyabout 80° C. to about 150° C.

The pressure of the system is correlated with the temperature range toassure that the petroleum gas is maintained in the liquid statethroughout the process. Preferably, the pressure is about 50 to about500 psig, most preferably about 100 to about 400 psig.

The amount of calixarene complexing agent to be used in the presentinvention will vary depending on such factors as, for example, theconcentration of carbonyl sulfide existing in the liquefied gas stream,the hydrocarbon composition of the gas stream, the particular calixarenecomplexing agent used, the nature of the contactor system and thecontact time, temperature and pressure.

Generally, the amount of calixarene is that amount effective to removeand achieve the desired level of carbonyl sulfide removal. Such amountis easily determined by one skilled in the art through routineexperimentation. For example, p-t-butylcalix[4]arene has a carbonylsulfide uptake factor of 0.41. This means that for every gram ofp-t-butylcalix[4]arene that is contacted with carbonyl sulfide containedin a petroleum gas stream, 0.41 grams of carbonyl sulfide will becomplexed. In terms of moles, the ratio of carbonyl sulfide top-t-butylcalix[4]arene is 4.42. Consequently, eachp-t-butylcalix[4]arene molecule is capable of complexing 4.4 carbonylsulfide molecules.

As will be obvious to one skilled in the art, the period of time forintimately contacting the calixarene complexing agent with the crudepetroleum gas stream will vary depending upon the amount of carbonylsulfide desired to be removed. In general, the petroleum stream iscontacted with complexing agents from about 0.3 to about 1 minute.

Once the carbonyl sulfide is complexed on the calixarene complexingagent the complex may be isolated from the purified gas stream usingconventional separation techniques, such as filtration, decanting,centrifugation and the like. Following isolation, the complex may begently heated to release carbonyl sulfide and regenerate the complexingagent. In general, the complex is heated at a temperature of about 85°C. to about 150° C. for about 20 minutes to about 2 hours to retrievethe calixarene complexing agent. The retrieved complexing agent may bereused in subsequent carbonyl sulfide removal treatments.

It should be understood that the process of the present invention is notto be limited to the use of the invention as described above, andmodifications within the foregoing description can be made while stillfalling within the spirit of the present invention. For example, it ispossible to perform the present invention by simply mixing thecalixarene complexing agent with a liquefied petroleum gas containingcarbonyl sulfide as an impurity in any suitable mixing tank underconditions sufficient for formation of the carbonyl sulfide/calixarenecomplex, and thereafter separating the carbonyl sulfide-free gas fromthe complex.

Other features of the invention will become apparent in view of thefollowing Examples which are given for illustration of the invention andare not intended to be limiting thereof.

EXAMPLE 1

A simple manifold was constructed to allow controlled contact betweencarbonyl sulfide and p-t-butylcalix[4]arene. Approximately 0.01 grams ofp-t-butylcalix[4]arene was placed in a stainless steel fitting in themanifold. The manifold was pressurized with carbonyl sulfide at 165 psiand allowed to equilibrate for 1 hour. At the end of the hour themanifold was depressurized and the carbonyl sulfide vented.

Subsequent analysis with Fourier transform infrared spectrometry (FTIR),using a potassium bromide pellet formed form the carbonyl sulfideexposed p-t-butylcalix[4]arene revealed that, in fact, a stable complexwas formed. Results are recorded in FIG. 2.

As shown in FIG. 2, the major carbonyl sulfide absorption was a packetcentered at 2061 cm⁻¹. In the spectrum of the exposedp-t-butylcalix[4]arene, this packet was shifted to 2022 cm⁻¹. This shiftin an inclusion complex was not unusual. This carbonylsulfide/p-t-butylcalix[4]arene peak (at 2022 cm⁻¹) persisted after thepellet was allowed to stand in ambient air overnight, and after thepellet had been reground. This indicated that the complex was verystable.

Temperature dependent measurements indicated that the complex could bedisrupted by gentle heating to 85° C. FTIR peak absorbance was monitoredas a function of time. Results were recorded in FIG. 3. The decrease inFTIR peak absorbance in FIG. 3 indicated the gradual release of carbonylsulfide from the complex.

EXAMPLE 2

The procedure of Example 1 was repeated but instead of mixing theexposed p-t-butylcalix[4]arene with potassium bromide for analysis byFTIR, the p-t-butylcalix[4]arene exposed to carbonyl sulfide was placedin a stream of humidified nitrogen. 100% relative humidity nitrogen waspassed over the exposed p-t-butylcalix[4]arene at a rate of 1.0 literper minute for 30 minutes. After exposure to humidified nitrogen, FTIRanalysis using a potassium bromide pellet formed from the carbonylsulfide exposed p-t-butylcalix[4]arene revealed that the carbonylsulfide was still present in the complex and had not reacted with thewater vapor.

EXAMPLE 3

The uptake level of carbonyl sulfide by p-t-butylcalix[4]arene wasdetermined.

76.914 mg of p-t-butylcalix[4]arene was weighed into a boat in amanifold. The boat was exposed to carbonyl sulfide at 165 psi for 1hour. The boat was removed and placed on an analytical balance tomeasure the weight loss as a function of time. Results are shown in FIG.4.

Initially, the mass of the exposed p-t-butylcalix[4]arene was 109 mgwhich indicates that the capacity for carbonyl sulfide uptake byp-t-butylcalix[4]arene is significant. The uptake factor was determinedto be 0.41. This means that for every gram of p-t-butylcalix[4]arenethat is exposed, 0.41 grams of carbonyl sulfide is complexed. This is afar higher uptake that would be expected from a simple adsorbent. Over130 minutes, the uptake factor fell to 0.12 which corresponds to theformation of a 1:1 complex of carbonyl sulfide/p-t-butylcalix[4]arene.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teaching. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

We claim:
 1. A process for the removal of carbonyl sulfide fromliquefied petroleum gas stream, which method comprises contacting (a) aliquefied petroleum gas containing carbonyl sulfide as an impurity; and(b) a calixarene complexing agent in an amount sufficient to remove saidcarbonyl sulfide from the petroleum gas stream; and recovering thecarbonyl sulfide-free liquid petroleum gas stream.
 2. The process ofclaim 1 wherein the liquefied petroleum gas and the calixarenecomplexing agent is contacted at a temperature and pressure effective toretain said petroleum gas stream in the liquid state.
 3. The process ofclaim 2 wherein the contact is carried out at a temperature of about 40°C. to about 200° C.
 4. The process of claim 1 wherein the calixarenecomplexing agent is of the formula I

wherein R₁-R_(3+n) are each independently H, primary C₁₋₂₀ alkyl,secondary C₃₋₂₀ alkyl, tertiary C₄₋₂ ₂₀ alkyl, C₁₋₂₀ alkoxy, C₁₋₂₀thioalkyl, C₆₋₂₀ aryl, C₆₋₂₀ aryloxy, C₆₋₂₀ aryl, nitro, halogen andCH₂NR₂ ¹ where R¹ is a C₁₋₂₀ alkyl; X₁-X_(3+n) are each independently H,OH, SH, C₁₋₂₀ alkoxy, C₁₋₂₀ thioalkyl, C₆₋₂₀ aryloxy, OC(O)C₁₋₂₀ alkyland C₂₋₂₀ alkenyloxy; and n is an integer of 1 to
 5. 5. The process ofclaim 4 wherein n is
 4. 6. The process of claim 5 wherein the calixarenecomplexing agent is a para-substituted calix[4]arene.
 7. The process ofclaim 6 wherein the calixarene complexing agent isp-t-butyl-calix[4]arene.
 8. The process of claim 1 wherein thecalixarene complexing agent is a solid.
 9. The process of claim 1wherein the calixarene complexing agent is immobilized on an inertsupport.
 10. The process of claim 1 wherein the calixarene complexingagent is used in an amount sufficient to remove substantially all of thecarbonyl sulfide from the liquefied petroleum gas.
 11. The process ofclaim 1 wherein the liquefied petroleum gas comprises a liquidhydrocarbon selected from the group consisting of propane, butane andmixtures thereof.
 12. The process of claim 11 wherein the liquidhydrocarbon further comprises hydrocarbons selected from the groupconsisting of ethane, propylene, isobutane, butene, pentane and mixturesthereof.
 13. A process for the removal of carbonyl sulfide from a liquidhydrocarbon, which method comprises contacting (a) a liquid hydrocarboncontaining carbonyl sulfide as an impurity; and (b) a calixarenecomplexing agent in an amount sufficient to remove said carbonyl sulfidefrom the liquid hydrocarbon; and recovering the carbonyl sulfide-freeliquid hydrocarbon.